Grand Teton National Park Geology

Imagine visiting Grand Teton National Park 85 million years ago. You would see a much different landscape. Stretching before you would be a great inland sea, which deposited layers of sediment on top of 2.4 billion year old granites and 2.8 billion year old gneisses. Jump forward 25 million years; those seas have retreated, and a major event, the Laramide Orogeny, is forming the Rocky Mountains. The Teton Range lies hidden beneath the unbroken surface and is waiting for a much younger and different series of events. The Teton Fault spans the entire length of the Teton Range's eastern front. Sometime between two to thirteen million years ago marked the beginning of uplifts, accompanied by a series of a few thousand earthquakes along that fault. These sporadic bursts of energy created the abrupt front of the Teton Range as it faces Jackson Hole. At 13,770 feet, the summit of the Grand Teton towers nearly 7,000 feet above the valley floor.

Total vertical displacement along this fault has been close to 23,000 feet. The valley of Jackson Hole dropped 16,000 feet, more than twice as much as the mountains rose. The beauty of the Teton Range lies in its majestic size and rugged appearance. Beginning as early as 2 million years ago, glaciers scoured and sculpted the Teton landscape. Large masses of ice flowed from the topographic high of the Yellowstone Plateau down into the valley of Jackson Hole. Fingers of ice, pulled by gravity, flowed from the high Teton peaks down into the valley. Grand Teton National Park contains piedmont lakes, U-shaped canyons, knife-like ridges, kettles, moraines, and other glacial features. Grand Teton National Park, as it is today, boasts dramatic vistas and a geologic story that is by no means over. This story still involves active geologic forces including glaciers, but the Teton Fault lies dormant. There has been a gap in seismic activity along the fault, but eventually it will lurch into action. Imagine a rubber band that is stretched to its limit; sooner or later it will break. For the Teton Fault it is not a matter of if, but when, it will move again.

Adapted from "Windows into the Earth"

by Robert B. Smith and Lee J. Siegel

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